Magnetic alloys



Patented July 11, 1950 MAGNETIC ALLOYS Ethan A. Nesbitt, Chatham, N; .I-.,, assignor to Bell" Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application August 5, 1948, Serial No..42,'131

4 Claims.

lar' the'present invention relates to alloys comprlsi'ngcobalt, molybdenum, chromium, and iron,

and to permanent'magnets made therefrom.

Anv object of this invention is the production of better and more efficient permanent magnet materials.

The permanent magnet alloys of the present invention are capable of being mechanically shaped, as by hot swaging, and possess maximum energy products and. electrical resistivities which are high as compared to permanent magnet materials'in common use.: They are, moreover, termed of relatively cheap and. available materi'als. V

The alloys of the present invention are: formed of cobalt, molybdenum, chromium and iron together with incidental'impurities, in the proportions of from 2 per cent to per cent cobalt, from 1'4.v per cent war per' cent molybdenum, from 3 per cent to 6 per cent chromium and the remainder iron except for incidental impurities. The desirable properties of the alloys ar developed by an initial high temperature heat treatment followed by quenching and a second heat treatment at a lower temperature. The initial heat treatment may be effected by maintaining the alloy at a temperature of from about 1150 C. to about 1350" C., and preferably at a temperature between 1200 C. and 1300 C., for a suitable period of time, ordinarily from about twenty minutes to about one hour or more. This initial heat treatment is carried out in an atmosphere which will not cause undesirable oxidation of the body of alloy, such as an atmosphere of hydrogen, methane :or city gas. The small amounts of oxygen which are present in city gas have the effect of decarburizing the alloy but are not sufficient to cause any significant oxidation of the metal itself.

The quenching which follows the initial heat treatment may be carried out in any suitable manner, as by immersing the alloy, at substantially the temperature of heat treatment, in a body of oil maintained at substantially room temperature.

The final heat treatment following quenching may vary from a treatment in which the alloy is maintained for several hours at 550 C. to a treatment in which the alloy is maintained at 800 C. for a few minutes. Ordinarily it is not practical to heat treat at below 550 C. since an unduly long heating time is required. It is not desirable to use a temperature above 800 C. be-

' m.l per cent.

2 cause of the diffl'culty of control. Ordinarily itis more desirable to use temperatures not exceed ing 750 0. Best control, with a practical heating time, is achieved with temperatures of from 625 C. to. 685 C. Within this temperature range, a satisfactory heating time is about one hour, although the heating may be continued for longe if desired.

A preferred alloy of the present: invention comprises from T2 to 74 per cent iron, from 4.5 to 5.5 per cent cobalt, from 16 to 18 per cent molybdenum, and from 4.5 to 5.5 per cent. chromium.

The amount of carbonpresent is preferably less than 0.05 per cent, and should not be more than A higher percentage. of carbon would. tend. to lower the coercive force and the residual induction of the alloy. Other impurities commonly found in magnetic alloys may be present in. small amounts, although. it is preferable to keep these. to a minimum, such as less than 1 per cent. Manganese may be present inamounts of 0.3 to 0.5 per cent to remove the free sulfur.

The following data are given to illustrate the improvement obtained in the alloys of the present invention over the commonly used magnetic alloys of iron, molybdenum, and cobalt. A composition containing 79 parts iron, 16 parts molybdenum, and 5 parts cobalt, when heat treated in the manner described above, had a residual induction after saturation of 9800 gauss, a coercive force of oersteds, and a BrHc product of 1,570,000. When 5 per cent of the iron in this alloy was replaced by 5 per cent of chromium, the Brl-Ic product was 2,450,000. Thus by replacing 5 per cent of th iron with chromium, the BrHc figure of merit was increased 56 per cent.

In another specific case, it was found that a composition containing 71 parts of iron, 17 parts of molybdenum, and 12 parts of cobalt, had a resistivity Of 45 microhm-centimeters. six per cent of the cobalt of this composition was replaced with 1 per cent of iron and 5 per cent of chromium, to produce a composition containing 73 parts of iron, 16 parts of molybdenum, 6 parts of cobalt, and 5 parts of chromium, which was heat treated in the same manner as the firstmentioned composition. The latter composition had a resistivity of 62 microhm-centimeters. Thus by replacing some of the cobalt of the firstmentioned composition with chromium and iron, a 38 per cent increase in the resistivity was obtained.

The following table gives further data on the results obtained with various alloys of the present invention. The (BH)m is the maximum energy 3 product, which on the demagnetization side of the hysteresis loop, is the product of induction B and magnetizing force H where this product is the greatest.

4 and from '72 to 74 per cent of iron, except for incidental impurities.

4. An article having properties adapted for permanent magnet use composed of an alloy con- The alloys of the present invention may be hot swaged and hot formed and may be prepared in various forms such as rods and bars. The finished magnets may be magnetized by any of the .usually employed methods.

Various changes and modifications may be made in the disclosed embodiments without departing from the spirit and scope of the invention.

What is claimed is:

1. A permanent magnet alloy consisting of from 2 per cent to 10 per cent cobalt, from 14 per cent to 21 per cent molybdenum, and from 3 per cent to 6 per cent chromium, the remainder being iron except for incidental impurities.

2. A composition according to claim 1 which is 35 1,927,940

quenched from a temperature of from 1200 C. to

-'1300 C., and then heated at about 625 C. to about 3. A permanent magnet alloy composed of from 4.5 to 5.5 per cent cobalt, 4.5 to 5.5 per cent chromium, from 16 to 18 per cent molybdenum,

2o taining from 4.5 to 5.5 per cent cobalt, from 4.5 to

5.5 per cent chromium, from 16 to 18 percent molybdenum, and from 72 to '74 per cent of iron, said alloy treated by a method comprising heating to from about 1200 C. to about 1300".C., followed by quenching, reheating to from about 6259' C. to about 685 C. and magnetizing; v ETHAN A. NESBITT.-

REFERENCES CITED The following references'are of record in the file of this patent: 1

UNITED STATES PAITENTSV I Date Number Name Koster Sept. 26, 1-933 2,082,041 Williams June '1, 1937 2,405,455 Seaver Aug. 6, 1946 FOREIGN PATENTS Number Country Date I Great Britain Nov. 16,1933 

1. A PERMANENT MAGNET ALLOY CONSISTING OF FROM 2 PER CENT TO 10 PER CENT COBALT, FROM 14 PER CENT TO 21 PER CENT MOLYBDENIUM, AND FROM 3 PER CENT TO 6 PER CENT CHROMIUM, THE REMAINDER BEING IRON EXCEPT FOR INCIDENTAL IMPURITIES. 